This invention relates to apparatus and methods for the manufacture of vehicle tires, and particularly to a vehicle tire-making drum having unique bead positioning, side wall formation and other features.
In the manufacture of vehicle tires it is common practice to lay up a carcass from layers of various fabrics on a rotating drum. It is also common in the industry to employ a drum in which the outer circumference (diameter) of the drum is adjustable, within limits, in preparation of the drum for receipt of the fabrics, for manipulation of the diameter of the drum in the course of formation of the carcass on the drum, for removal of the formed toroidal carcass from the drum, and/or for allowing a single drum to be employed for the manufacture of different diameter tires.
Most all vehicle tires include a pair of non-extensible bead rings which serve to define, in part, the internal diameter of the finished tire. Thus, the bead of a tire is that portion of the tire immediately adjacent the internal diametral region of the tire, and which is received by one side of the wheel rim of a vehicle. Each tire has two beads, one on each of the opposite sides of the tire. Bead rings commonly comprise a bundle of individual non-extensible metal rings or strands, similar to a metal cable.
Incorporation of the bead rings into a tire carcass has long been a troublesome aspect of a tire manufacturing process. Further, this operation is one of the more important operations in the process of manufacturing a vehicle tire in that the initial positioning of the bead rings of a tire establish that structural feature of a tire which is most critical to the success of the ultimately formed tire. That is, the bead rings must be initially positioned concentric to the rotational axis of the drum, must be disposed in respective essentially parallel spaced apart planes, such planes being oriented substantially perpendicular to the rotational axis of the drum. In achieving this initial disposition of the beads on a carcass formed on a rotatable drum, it is further necessary that the bead rings be secured (ie., bonded) to or within the carcass such that when the carcass is removed from the drum, the beads retain their initial orientation with respect to one another and to the carcass itself.
In the manufacture of radial and/or biased vehicle tires, in particular, securing the bead rings within the carcass requires that several factors be taken into consideration. First, after the body of the carcass is laid up on the drum, a bead ring is moved into encircling relationship to each of the opposite ends of the formed carcass. Once thus positioned, the drum is activated to xe2x80x9clockxe2x80x9d each bead ring in its encircling position about the carcass. This normally takes the form of radially expanding one or more components of the drum at each end of the drum to capture an end of the carcass between the expanding component(s) and a respective bead ring. This action sets the position of the bead rings relative to the rotational axis of the drum and relative to the then-existing axial positions of the bead rings relative to the drum. Employing the same drum, the carcass is expanded in the region thereof between the bead rings to at least partially define its desired toroidal shape. This action stretches the carcass, especially at its opposite ends where the bead rings are located. To accommodate the radial expansion of the carcass, the bead rings, which are initially axially outboard of the ends of the drum must be moved axially inwardly of the drum. Recalling that the locking of the bead rings to the drum results in capture of the carcass between the locking mechanism and the bead rings, under these conditions. there can be no sliding or other repositioning movement of the carcass relative to the bead rings, ie., they are locked together. In order to capture each bead ring within the carcass such that there is no relative movement between the bead rings and the carcass after the bead locks have been released and the carcass is removed from the drum, a portion of the carcass which projects axially outboard of the location of a bead ring is folded radially upwardly and axially inwardly of the drum to wrap the bead ring and then overlie the carcass where this annular flap is bonded to the central body of the carcass to thereby capture the bead ring in the fold so formed.
In the prior art apparatus and methods, relatively complex and costly apparatus (and accompanying process steps) must be taken to precisely move the bead rings axially inwardly of the drum as the carcass is radially expanded. In like manner, the apparatus and process steps employed heretofore for wrapping the outboard ends of the carcass about the bead rings and into overlying relationship to the central body portion of the carcass have involved complex apparatus and process procedures, all of which must preclude the wrinkling of the carcass as the locked bead ring (with the carcass locked and bonded in partial wrapping relationship to only the inner circumference of each bead ring , hence non-positionable relative the each bead ring) is moved axially inwardly of the drum as the carcass is expanded radially. Heretofore, these combined movements of the radial expansion of the carcass and axially inward movement of the bead rings have been basically accomplished by means of two (or more) independently-controlled subsystems of the drum. Thus, control over the bending and stretching of the carcass at the outboard ends of the drum has been lacking, as has been the ability to ensure non-wrinkling of the carcass as the locked bead rings and that portion of the carcass which is locked to the bead rings, thereby resulting in undesirable rejection rates of completed vehicle tires.
Desirably, in the formation of certain vehicle tires on a drum, after the carcass has been formed with at least partial sidewalls and beads, a further fabric is overlaid upon the carcass on the drum, commonly as a part of each sidewall. This procedure of first folding each end of the partially formed carcass is xe2x80x9cupxe2x80x9d (i.e., radially outwardly) from the drum to overwrap the bead rings and into overlying relationship to the carcass on the drum, and thereafter, applying an additional layer of fabric on the carcass and folding each end of this additional layer xe2x80x9cdownxe2x80x9d and about the bead rings and the formed sidewalls is commonly referred to as xe2x80x9cone up one downxe2x80x9d. The bonding of the downwardly folded ends of the additional layer to the axially outward surface of a respective sidewall is commonly carried out by means of a stitching wheel which serves to bond the added fabric to the first fabric of the sidewall. In the manufacture of these tires, to provide access to the outer surfaces of the sidewalls for stitching and/or other purposes, it is required that the bead locking subassembly of the drum be moved axially outwardly of the drum to provide an open space for the stitcher to enter and function. To successfully perform this operation, the expanded central portion of the carcass must remain expanded during this operation. Ensuring that the central portion of the drum with the partially formed carcass thereon does not collapse radially as the bead lock subassemblies release their locking of the bead rings and are moved axially away from the central portion of the drum to permit a stitching operation, has been accomplished in the prior art through the use of extensive mechanical mechanisms, some of which occupy inordinate volume of the interior of the drum and thereby limit the permissible radial expansion range of the drum.
It is therefore an object of the present invention to provide an improved drum for use in the manufacture of vehicle tires.
It is another object of the present invention to provide a method for the formation of a vehicle tire employing a rotatable drum.